Populations of sage-grouse have declined in recent decades, and the species’ range-wide distribution across western North America has been reduced to nearly half of its historic distribution. Although the rate of decline of this species has slowed over the past two decades, there is concern for the future of sage-grouse because of its reliance on sagebrush, which is a central component in an ecosystem that has been greatly altered during the past 150 years and is currently at risk from a variety of threats. Not only are healthy stands of sagebrush necessary year-round for sage-grouse to survive, but, during summer, young sage-grouse also require a diverse understory of native forbs and grasses. This vegetation provides protection from predators and supplies high-protein insects necessary for rapidly growing chicks.
In 2014, DOE-ID entered into a CCA with the U.S. Fish and Wildlife Service (USFWS) to conserve sage-grouse and the habitats that it depends on across the INL Site (DOE-ID and USFWS 2014). This voluntary agreement established a Sage-Grouse Conservation Area (SGCA) where infrastructure development and human disturbance would be limited (Figure 1). To guard against sage-grouse declines, the CCA includes a population trigger that, if tripped by declining male lek attendance, would initiate an automatic response by both the USFWS and DOE-ID. The population trigger would trip if there is a 20 percent or greater reduction in the three-year average peak male attendance on a set of 27 baseline leks within the SGCA.
The CCA established a monitoring program based on this trigger threshold and other criteria. Part of the program includes annual surveys of sage-grouse leks on the INL Site. A lek is a traditional breeding site, located near a nesting habitat, where sage-grouse return each spring to display and mate. Counting males annually at lek sites is the best way to document trends in sage-grouse abundance. Because sage-grouse abundance varies naturally from year to year, biologists use a three-year running average of the peak male attendance across 27 baseline leks to calculate trends relative to the population trigger.
In 2013, DOE-ID formalized the following three monitoring tasks designed to track the number of male sage-grouse at active leks and document additional active leks on the INL Site. The general tasks and their purposes are:
Historical Lek Surveys — Surveys of sites where sage-grouse have been observed displaying in the past. The purpose is to determine if grouse still use those areas.
Systematic Lek Discovery Surveys — Surveys of poorly sampled regions of the INL Site. The purpose is to discover additional active leks, especially within the SGCA.
2015 Lek Surveys
In 2015, ESER biologists surveyed all 47 leks classified as active on or near the INL Site from two to seven times each. These leks were partitioned into three different categories for analysis, with some leks occurring in more than one category.
SGCA Baseline Leks: With regard to the CCA population trigger, the most important category consists of the 27 leks that were used to establish the original baseline value upon which the trigger is based. The sum of peak male attendance counts across the 27 leks in 2015 was 335, and the three-year mean (2013–2015) was 340. That mean is identical to the 2014 mean (Figure 2), and remains at 134 percent of the population trigger point (i.e., 253 males—based on data from 2011). Twenty of the 27 baseline leks remain active after two were reclassified as inactive in 2015. In each of the past three years, two or three baseline leks per year have been reclassified as inactive as an improving data set provides a more accurate picture of the activity status for each lek. These results should not be interpreted as evidence that seven leks have been abandoned in the past three years, but rather that five years of data have accumulated for most leks, allowing for more precise lek classifications.
Non-Baseline Leks: All other known active leks—whether in or out of the SGCA—that are not part of the baseline set described above fall into a second analysis category. In 2015, 23 Category 2 leks were classified as active following the breeding season. On these leks, we observed 244 males at peak attendance. By comparison, in 2014 we counted 264 males on 20 active leks outside the SGCA.
Lek Routes: The third category includes all leks, both active and inactive, that are part of three lek routes established by the Idaho Department of Fish and Game. These routes—Lower Birch Creek, Tractor Flats, and Radioactive Waste Management Complex (RWMC)—have been monitored annually since 1999, and they provide historical context for interpreting abundance trends on the INL Site.
Summed peak male attendance across the three lek routes was 254. This count is slightly lower than the 2014 peak of 260 males but still higher than any other year since 2010 when the largest wildland fire in INL Site history occurred (Figure 3). Both the Lower Birch Creek and the Tractor Flats routes had higher counts of males in 2015 than in recent years (n = 82 and 76, respectively). The Lower Birch Creek count was higher than any year since 2007, and the Tractor Flats count was the highest since the Jefferson Fire (2010). Peak male attendance on the RWMC route was 96 males, a moderate decrease following two consecutive years of increased attendance.
Historical Lek Surveys
During the past several decades, many leks on the INL Site have been documented by researchers and the Idaho Department of Fish and Game as a result of surveys and opportunistic observations of displaying sage-grouse. Prior to 2009, many of these historical lek sites had not been surveyed for nearly 30 years. For the past seven years, ESER biologists have revisited a subset of historical leks each spring to determine if the leks remain active based on current criteria. The objective has been to determine which historical leks remain active before ESER establishes new lek routes prior to the 2017 lek season.
We surveyed 15 historical leks in the SGCA an average of 2.2 times (range: 2–3 surveys) and 11 historical leks outside the SGCA an average of 2.3 times (range: 2–3 surveys). Across those 26 potential lek sites, we observed males displaying on one lek on two separate visits (three males during one visit and one male during another visit) and four males displaying on another lek during a single visit. Consequently, these two leks were reclassified as active.
After a historical lek has been surveyed for five years without at least two years of observed breeding activity, it is reclassified as inactive. Following the 2015 survey season, 10 leks were reclassified as inactive. Fourteen leks remain classified as historical and will be surveyed again in 2016.
Systematic Lek Discovery Surveys
Known lek sites are few or absent across large portions of the SGCA even though habitat in these areas often appears to be adequate to support sage-grouse breeding and nesting activities. Since 2013, ESER has systematically searched for unknown lek sites each spring in areas where few or no leks are known. The objective of this task is to continue to search for active lek sites in an effort to find as many as possible before new lek routes are established.
In 2015, we completed 74 surveys (29 road, 45 remote) within the northeastern section of the INL Site and discovered one sage-grouse lek. We counted two males on one visit to the new lek and three males on a second visit, and on both occasions we observed from four to 14 other sage-grouse of unknown gender. Since discovery surveys commenced in 2013, ESER has discovered four previously unknown leks.
Sage-Grouse Abundance - Summary & Conclusions
Prior to the start of the 2015 field season, 47 leks were classified as active on or near the INL Site, including two just outside the site boundaries that are part of the IDFG survey routes. In 2015, we reclassified two active lek sites as inactive. However, we added three new active leks to the list (two confirmed during historical lek surveys and one documented during the lek discovery surveys), increasing the total number of known active leks on or near the INL Site to 48 (Figure 1). In 2009, only 26 leks were known to be active on the INL Site. Although some lek sites may have become occupied since 2009, the majority of leks were simply discovered or rediscovered through the ESER program’s systematic effort.
Peak male attendance in 2015 across all leks on the INL Site was 589. This count represents the summed counts from SGCA baseline leks (n = 335), all other active INL Site leks recognized as such at the beginning of the field season (n = 244), the two historical leks reclassified as active in 2015 (n = 7), and the newly discovered lek (n = 3). For greater detail on the 2015 sage-grouse monitoring season, see Implementing the Candiate Conservation Agreement for Greater Sage-Grouse on the Idaho National Laboratory Site: 2015 Full Report.
The population trigger for sage-grouse will trip if the three-year average of peak male attendance falls below 253 males across the 27 baseline leks within the SGCA since this would represent a decrease of over 20 percent of the 316 males counted in 2011. The three-year average peak male attendance (2013–2015) on the 27 baseline leks remains at 340 individuals—the same as last year’s three-year average. Therefore, this index shows no evidence that sage-grouse abundance is declining on the INL Site.